Signs of Low IQ in Adults and Children: Look-Alikes

Q: What are the signs of a low IQ?

Scores from 70 to 84 are usually described as below average or borderline, and about 14% of people score in that range. A score around 70 or below is one of the criteria for intellectual disability, alongside difficulties with everyday adaptive skills that begin in childhood.

Q: Eight things often mistaken for low intelligence

Yes. Dyslexia, ADHD, anxiety, depression, poor sleep, hearing or vision problems, testing in a second language and missed schooling can all make someone seem slower or struggle with tests without reflecting their underlying ability.

THE SHORT ANSWER

What are the signs of a low IQ?

With a lower score, unfamiliar material takes more repetition before it sticks. Multi-step problems take longer. Planning ahead and changing tack mid-task both cost more effort.

None of which settles anything. Every sign here has a duller explanation available: untreated hearing loss, poor sleep, depression, a test sat in a second language. IQ is only measured properly by a trained examiner working through a full battery.

HOW INTELLECTUAL DISABILITY IS DIAGNOSED (DSM-5)A low score on its own isn't enough: all three gates must apply.

GATE 1Low intellectual functioningUsually an IQ around 70 or below (about two standard deviations under the mean), allowing for measurement error.

GATE 2Difficulties with adaptive skillsEveryday conceptual, social and practical skills, such as money, communication and self-care, need support.

GATE 3Onset in childhoodThe difficulties begin during the developmental period, not after an illness or injury in adulthood.

All three present: a diagnosis can be consideredMiss any one gate and it isn't intellectual disability.

THE PATTERNS, AND THEIR LOOK-ALIKES

Six patterns that can accompany lower scores

The patterns below cluster at lower scores without belonging to them. Each carries its ordinary alternative underneath.

Learning new things slowlyNeeding more explanation and repetition than peers to master new skills or information.

ALSO CAUSED BY

DyslexiaMissed schoolingSecond language

Difficulty with abstract problemsFinding hypothetical questions, analogies or rules hard without concrete examples.

ALSO CAUSED BY

AnxietyUnfamiliar test format

Trouble with multi-step tasksLosing track of instructions or steps, especially when given all at once.

ALSO CAUSED BY

ADHDHearing problemsPoor sleep

Difficulty planning aheadStruggling to organise time, money or future steps.

ALSO CAUSED BY

ADHDDepression

Struggling to adapt to changeFinding new routines, places or rules harder than most.

ALSO CAUSED BY

AutismAnxiety

Limited vocabularyUsing fewer and simpler words, and finding complex text hard to follow.

ALSO CAUSED BY

Second languageFewer books at homeDyslexia

LOOK-ALIKES

Eight things often mistaken for low intelligence

Choose one to see how it can show up in daily life, plus the detail that separates it from a general learning difficulty.

Dyslexia

CAN LOOK LIKESlow, effortful reading and poor spelling, so written tests and homework go badly.

THE TELL-TALE CLUESpoken understanding and reasoning are often normal or strong; the gap is specific to reading and spelling.

A specialist literacy assessment can identify it. Many tests can be given orally.

A SCORE ISN'T FIXED

What moves IQ scores, and by how much

Four things move the number by a known amount. An extra year of education adds 1 to 5 points, from Ritchie and Tucker-Drob's 2018 meta-analysis of natural experiments. Severe childhood iodine deficiency takes 12 to 13 off. The Flynn effect put roughly 3 points on per decade through the twentieth century, so a score from 1950 and a score from 2020 are not the same thing.

Each extra year of educationMeta-analysis of natural experiments (Ritchie & Tucker-Drob, 2018).+1 to 5

A decade of the Flynn effectAverage gain per decade across the 20th century in many countries.≈ +3

Severe iodine deficiencyChildren in deficient areas score lower on average, in meta-analyses.−12 to 13

Testing in a second languageVerbal subtests in particular underestimate ability; size varies widely.varies

Scale 0–15 points. Ranges show the spread across studies.

A note on wordsClinicians use "intellectual disability" and "borderline intellectual functioning". Older labels are now considered offensive. A score describes performance on one test, not a person's worth, character or potential to learn and live well.

QUESTIONS PEOPLE ASK

Four answers, at a glance

7085100130

70–84 · 13.6% of peopleunder 70 · 2.3%

What is considered a low IQ?70 to 84 is usually called below average or borderline. Around 70 or below is one criterion for intellectual disability, never the only one.

Work

Own home

Family

Can someone with a low IQ live independently?Yes. Many people with below-average IQs, and many with mild intellectual disability, work, live on their own and raise families, sometimes with support in specific areas.

Education

Practice

Sleep

Health care

Can IQ be improved?Yes. More education reliably raises scores, and regular practice of reasoning and memory skills builds them. Treating poor sleep, hearing loss or depression can also restore performance that was being held back.

Test nerves

Unfamiliar format

Second language

↓ scorewithout any change in ability

Should I worry if I struggle with IQ tests?Not on its own. Nerves, unfamiliar formats and language all pull scores down. If everyday life is genuinely hard, a psychologist can look at the whole picture.

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